Avoid altering the internal encoding.

Author: udan11

src/Lexer.php

@@ -42,13 +42,6 @@ function __($str)
         define('USE_UTF_STRINGS', true);
     }
 
-    // Set internal character to UTF-8.
-    // In previous versions of PHP (5.5 and older) the default internal encoding is
-    // "ISO-8859-1".
-    if ((defined('USE_UTF_STRINGS')) && (USE_UTF_STRINGS)) {
-        mb_internal_encoding('UTF-8');
-    }
-
     /**
      * Performs lexical analysis over a SQL statement and splits it in multiple
      * tokens.
@@ -192,7 +185,7 @@ public function __construct($str, $strict = false)
             // For multi-byte strings, a new instance of `UtfString` is
             // initialized (only if `UtfString` usage is forced.
             if (!($str instanceof UtfString)) {
-                if ((USE_UTF_STRINGS) && ($len != mb_strlen($str))) {
+                if ((USE_UTF_STRINGS) && ($len !== mb_strlen($str, 'UTF-8'))) {
                     $str = new UtfString($str);
                 }
             }

src/Token.php

@@ -250,18 +250,18 @@ public function extract()
         case Token::TYPE_STRING:
             $quote = $this->token[0];
             $str = str_replace($quote . $quote, $quote, $this->token);
-            return mb_substr($str, 1, -1); // trims quotes
+            return mb_substr($str, 1, -1, 'UTF-8'); // trims quotes
         case Token::TYPE_SYMBOL:
             $str = $this->token;
             if ((isset($str[0])) && ($str[0] === '@')) {
-                $str = mb_substr($str, 1);
+                $str = mb_substr($str, 1, null, 'UTF-8');
             }
             if ((isset($str[0])) && (($str[0] === '`')
                 || ($str[0] === '"') || ($str[0] === '\''))
             ) {
                 $quote = $str[0];
                 $str = str_replace($quote . $quote, $quote, $str);
-                $str = mb_substr($str, 1, -1);
+                $str = mb_substr($str, 1, -1, 'UTF-8');
             }
             return $str;
         }

src/UtfString.php

@@ -81,7 +81,7 @@ public function __construct($str)
         // overloading is enabled.
         // https://php.net/manual/ro/mbstring.overload.php
         $this->byteLen = strlen($str);
-        $this->charLen = mb_strlen($str);
+        $this->charLen = mb_strlen($str, 'UTF-8');
     }
 
     /**